Cisco 3650 IOS-XE reports IP address overlap - masking bug?

[noemi.berry]

Am I losing my mind?  Brand-new stacked Cisco 3650s reporting an IP address overlap where there clearly iisn't one!  This eensy little /29 doesn't come close to the lower edge of the /20 space.

This config looks innocent enough:

interface Vlan128

 ip address 10.1.128.1 255.255.255.248

!

interface Vlan130

 ip address 10.1.130.1 255.255.240.0

But the switch reports an IP address overlap during configuration, and won't accept Vlan130:

Switch#conf t

! defaults, these don't apply, but just covering this base

Switch(config)#ip classless

Switch(config)#ip subnet-zero

Switch(config)#interface Vlan128

Switch(config-if)# ip address 10.1.128.1 255.255.255.248

Switch(config-if)#interface Vlan130

Switch(config-if)# ip address 10.1.130.1 255.255.240.0

% 10.1.128.0 overlaps with Vlan128

If I change the clashing IP address to 10.1.144.1 /20, it's accepted.

This occurs on two new stacks, running:

    Cisco 3650 IOS-XE Version 03.07.01E

    Cisco 3650 IOS-XE Version 03.03.05SE

Is this a known bug?  Have I and numerous other IP calculators completely forgotten how to do IP subnetting ?

[Jon Marshall · Accepted solution]

It does overlap.

The network for 10.1.130.1 is 10.1.128.0 and the available hosts are 10.1.128.1 -> 143.254 with 10.1.143.255 being the broadcast.

That's also the reason why your 10.1.144.1/20 works because it is the next available network with a 255.255.240.0 mask

Jon

[noemi.berry]

aw, crap, of course.  Where did the /20 mask on 10.1.130.0 come from?!  Some combination of outdated documents and an inability to think.

Very silly, thank you.  Duh.